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-------------- Original message from Alexandre E Eremenko <eremenko@MATH.PURDUE.EDU>: --------------


> Joel,
> Your questions give me an opportunity to describe my
> limited experience in detail.
>
> 1. First I found, to my surprise, that it is hard to
> find a place for a sextant in a 42 feet boat:-)
> I mean, to have the sextant box in a secure place, and at the
> same time, easily accessible. Finally I put it on a little shelf
> (with a board) in my cabin, and secured the box with towels
> to prevent it from moving horizontally. But opening the box, taking the
> sextant out and storing it back was a substantial hussle.
> I appreciated the relatively small size of the box of my sextant,
> and I disagree with Bauer who says in his book that he prefers boxes
> which allow the st! orage of the sextant with a telescope attached.
> This may be a luxury for big ships, but not for a small boat.
> (The largest boxes I've seen so far are those of C. Plath,
> almost the size of a siutcase:-) and the smallest ones are
> of some Hughes "Mate" sextants.
>
> 2. Second, a major difficulty was to carry my sextant around
> in a rolling boat from my cabin to the cockpit and back.
> As the boat was rolling violently, I had to use my one hand
> to hold a rail (or someting else) balancing the sextant in another hand,
> anxious not to kick it against anything in the sudden moves of the
> boat. Immediately after observation, I had to carry the sextant
> back to my cabin, because there was no secure place to put it in the
> cockpit.
>
> I experimented with fixing the whole box outside, on the cabin's
> roof, under the tent, but this did not work because it inter! fered with
> the ropes, tent, etc.
>
> 3. It was very hard in the first two days indeed.
> So hard that I had to make most observations without a scope
> in these first days. And had hudge blunders and errors.
> (I already mentioned that the zero-magnification tube
> seems to be absolutely necessary for observations without
> a scope, and I did not have it). We sailed before
> the wind, at 6 to 8 knots, with pretty large waves,
> possibly 10 feet by my estimate, and the
> boat was rolling, pitching and yawing very much.
>
> Yawing motion is the most unpleasant for sextant observations,
> especially with an inverting scope:-)
>
> 4. However I adapted quickly. (Or maybe the sea was not so rough
> in the subsequent days). The best results were achieved when we
> sailed to windward and rolling was not so strong.
>
> Anyway, in the first week! of August I was able to obtain
> decent results with my favorite inverting scope.
> I found that the wires help to keep the sextant vertically:
> you align the horizontal wire with the horizon.
> "Rocking" is more precise, of course, but it was not always possible
> when the boat was rolling like crazy.
>
> 5. I found that the best position in the rough sea for observation was
> sitting on the cabin roof close to the mast, leaning with my
> back to the mast
> (tied to a railing with a harness, but this was mostly for
> phychological
> reasons). Soon I will post a picture of myself doing this.
>
> The hardest part was to keep the Sun and the horizon in
> the field of view for the time necessary for observation.
> I understand that inverting scope makes it much harder,
> so only now I fully understand the complains of the list members
> about the inver! ting scope:-) The problem was not present on land.
>
> I believe that standing at the same place would be better,
> but I found no way to fix my body in standing position,
> with both hands free, and feeling stable enough.
>
> The reason why standing positiuon is preferred is that
> in low position the waves frequently obscure the horizon.
>
> 6. On smaller waves I found it most convenient sitting on
> the windward cockpit bench, with my feet pressing against the table
> in the center of the cockpit (on smaller yachts, the opposite
> bench can play this role).
>
> 7. The procedure was usually this. I came to the cockpit with the scope
> detached (in my pocket). Another pocket contained a little notebook
> and a pencil. Sextant held in the right hand,
> and attached with a strap to my neck. For the timing, I used my
> waterproof wristwatch.
> > First I put the darkest shade on the horizon mirror
> and aim it at the sun (without the scope) holding the sextant
> upside down. Keeping the Sun in view, I moved the arm until I could
> see the horizon. Then I attached the scope, engaged a dark filter
> on the index mirror and changed the filter on the horizon mirror
> for a ligter one. Keeping the sextant upright, now I tried to achieve
> a decent touch. (But of course both the Sun and the horizon try
> to escape all the time from my field of view in all directions:-)
> After I had a satisfactory touch, I looked at the watch memorizing the
> seconds first. Then, sextant hanging on a strap on my neck,
> I pulled the notebook and pencil, recorded the time, and after that,
> the sextant reading. This I tried to repeat 3-5 times, until
> the Sun hided behind the clouds, or my hand got tired
> (I really appreciate the light weight! of my sextant).
> Then I had to walk and record the GPS reading for control.
>
> 8. Very frequently the sextant was splashed by sea water in the process.
> So after each observation I had to rinse the mirrors and the shades
> with fresh water, and add a little oil to the drum.
> (Otherwise, next time the drum assembly will be stuck and will
> move only with an effort. First time it was stuck so strongly that I had
> to add oil before I could move it.)
>
> But even during the observation, the water drops on the mirrors
> and shades sometimes had to be wiped because they interfere with the view.
>
> 9. To answer your question, I never asked to change the course,
> or anything else, to accomodate my observation. And never used
> an assistant, even to look at GPS.
> It was important who steered the boat: with a more experienced helmsman
> the boat yaws much les! s, and yawing was a major nuisance, as I said
> before.
>
> Following the Russian manual I observed the stars with my upright scope
> and Sun with the inverting scope. But only once there was an opportunity
> to observe the stars.
>
> Besides my sextant and watch, I carried only a notebook,
> a pencil, the Almanac and Casio calculator.
> (No reduction tables).
>
> 10. I consider the enclosed screw a drawback of SNO/Freiberger
> sextants. Maybe it protects from dust but not from the splashes of
> sea water. And you cannot wipe the mechanism, and you cannot even see it.
> The only thing you can do is to add some oil.
>
> 11. My "dream sextant" will have three scopes: a straight Galileo one
> some 3.5 times 50, an inverting one with wires, 6 to 8 times 40,
> a zero magnification tube (or better a "pinhole" of the old British
> sextants), several e! yepieces for various magnification,
> and an eyepiece filter. It will have an open screw assembly,
> classical split view mirror, and a small box.
>
> I am aalso very curious to try a sextant with a nonius assembly
> instead of the worm screw. I've seen some outstanding examples
> in the antique shops and museums in Europe.
> I understand that this is harder to read, but the whole mechanism
> seems to me much more robust and reliable.
> (Because there is no wormscrew-and-tooth assembly which is vulnerable
> to wear, dust, small insects and sea salt:-)
>
> Alex.
>
> On Tue, 9 Aug 2005, Yourname Here wrote:
>
> > Alex,
> >
> > Since this was your first attempt to shoot from a small boat in rough
> conditions, it would be intersting to know what procedures you used to get your
> self postioned so that you were not concerned about f! alling or going overboard,
> and what else you did to get the best sight possible.
> >
> > I guess your skipper was more concerned in getting to his destination.
> Frequently, a change in course or heaving to, provides a much better platform.
> >
> > Joel Jacobs
> > --
> > Visit our website
> > http://www.landandseacollection.com
> >
> >
> >
> >
> > -------------- Original message from Alexandre E Eremenko
> : --------------
> >
> >
> > > For the first time I had an opportunity to use
> > > the natural horizon.
> > > I sailed from Dublin to Kiel, with stops in
> > > the Scilly Islands, the Isle of White and Helgoland,
> > > in a 42 feet sailboat, on July 23-August 6.
> > > Unfortunately, the weather was not good fo! r Cel Nav.
> > > For several days the Sun was not visible at all,
> > > on other days I had to use small gaps in the clouds.
> > > There was no oppornutity for Lunars, and I could make
> > > only one star observation, in unfavorable conditions.
> > >
> > > The first week was a disappointment (from the Cel
> > > Nav point of view); we sailed downwind with hudge waves,
> > > and I could only make observations without a scope.
> > > The results were very bad, but one has to take into account
> > > that these were my FIRST observations with natural
> > > horizon.
> > >
> > > One general remark on observations without a scope.
> > > I think, one HAS to use the zero-magnification tube.
> > > Otherwise, it is hard to make sure that your line
> > > of sight is parallel to the pl! ane of the arc,
> > > especially when the boat is shaking violently, and
> > > its course is not stable.
> > > This introduces a hudge "colimation error"
> > > which resulted in errors in position line of several minutes,
> > > once even 2 degrees, though I am not sure what exactly
> > > caused such blunder.
> > >
> > > In the second week, I achieved a tolerable precision.
> > > Maybe because of some practice, but more likely,
> > > because the weather improved.
> > >
> > > Here is the statistics of all my observations in the second
> > > week (August 1-6).
> > > I used my SNO-T sextant and Casio watch. Reduction with
> > > the Almanac and Casio calculator.
> > > The number in parentheses is the number of observations
> > > averaged; if there is no number > > > in parentheses, this means that only one observation
> > > was made. The number of minutes
> > > is the error
> > > in altitide (using GPS position as AP).
> > > August 1 Sun, 30 knots wind, waves 2-3 meters,
> > > course downwind: (5) -0.2'
> > > August 2 (Sun from a beach, Helgoland)
> > > (5) +0.5'
> > > (1) 0.0'
> > > (2) +0.5'
> > > (3) +0.5'
> > > August 4 Sun, good weather (15-17 knots wind, waves less
> > > than 1 meter): -0.1', -0.1',
> > > 0.1', -0.5',
> > > 0.3', -1.2', -0.8', -0.6', (3) -0.3'.
> > >
> > > The only star observation was on July 25:
> > > Venus (4), error -1.4' and Arcturus (1) error +3'.
> > >
> > > If anyone is interested, I can post (or send) the full detail
> > > of each ob! servation.
> > >
> > > I also tested my new Bris sextant which I bought at
> > > Cassens-Plath factory which I visited early in July.
> > > They said that the one I bought was the last one,
> > > its production being discontinued.
> > > I will write a separate message on the Bris sextant.
> > >
> > > Alex.